The invention relates generally to semiconductors and more particularly to the growth of nitrogen containing semiconductor material utilizing nitrogen halides as the nitrogen source.
Solar energy represents a vast source of relatively non-polluting, harnessable energy. It has been estimated that the amount of solar energy striking the United States each year is over 600 times greater than all the country""s energy needs. Despite this abundance, solar energy has proven difficult to economically collect, store, and transport and thus has been relatively overlooked compared to the other more conventional energy sources, i.e., oil, gas and coal. However, as conventional energy sources become less abundant and their detrimental effect on the environment continue to escalate (acid rain, air particulates, green house gasses, etc), solar energy is becoming a more viable and attractive energy source.
One of the more effective ways of harnessing solar energy is through photovoltaic or solar cells, which convert solar energy directly into electrical energy. The energy conversion, solar to electrical, mediated by photovoltaic cells relies on semiconductor materials having a p-n junction with a surface exposed to the sun light. Sun light energy strikes the semiconductor and xe2x80x9cfreesxe2x80x9d electrons in the surface material. This movement of electrons provides a current that can be used to power electrical devices. Presently, there is a need in the relevant art to have more cost effective and efficient photovoltaic cells. Cost effectiveness and the efficiency of photovoltaic cells are largely dependent on the cost of growing the semiconductor material and on the ability of the semiconductor material to efficiently convert solar energy to electrical energy.
The compounds used to produce compound semiconductors include elements listed in Group III and V or II and VI of the periodic table. A higher efficiency solar cell could be achieved if a high-quality material with a band gap of about 1 electron volt (eV) and a lattice technologies such as laser diodes that would benefit from the availability of semiconductor materials with a range of band gaps and lattice constants. Recently, it was shown that incorporating small amounts of nitrogen into GaAs results in a surprisingly large decrease in the material""s bandgap without much effect on the lattice constant. Kondow et at., 1996, Jpn. J. Appl. Phys. 35:1273-1275.
In general, there are two techniques used to grow semiconductor material, molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD). MME is a system that includes a deposition chamber maintained at low pressure, and has one or more effusion cells that contain material desired on the semiconductor wafer. The effusion cells are heated, which causes the atoms to evaporate out of the material and deposit onto the wafer located in the deposition chamber. Nitrogen has been successfully introduced into the MBE growth scheme by a radio-frequency plasma source which activates N2. Unfortunately, although this is an effective means for growing nitrogen containing semiconductors, it is slow and as a result relatively cost prohibitive, especially in the case of solar cells which require a relatively large area of semiconductor growth. As such, MBE has not proven desirable for the growth of photovoltaic cells.
MOCVD allows for faster crystal growth and is hence more cost effective. It produces a semiconductor material, for example GaAs, by flowing trimethylgallium (TMGa) and arsine into a reaction chamber to form GaAs. Unfortunately, the addition of nitrogen to the semiconductor material using MOCVD has not resulted in high quality semiconductor material. In addition, the nitrogen sources, e.g., hydrazine and dimethylhydrazine (DMH), have proven to be difficult to obtain in high purity, expensive and/or potentially dangerous. Against this backdrop the present invention has been developed.
In one aspect, the invention provides a method for growing nitrogen containing III-V alloys that includes providing a substrate for forming an epilayer of III-V alloy and forming the epilayer on the substrate utilizing metal-organic chemical vapor deposition. The nitrogen source is a nitrogen halide.
In anther aspect, the invention provides a semiconductor for a solar cell comprising a substrate and an epilayer of nitrogen containing a III-V alloy. The nitrogen containing alloy results from a metal-organic chemical vapor deposition, where the nitrogen source is a nitrogen
These and various other features as well as advantages that characterize the invention will be apparent from a reading of the following detailed description and a review of the associated figures.